The invention relates to an actuator for the reversible movement of a valve flap of a valve, and to a use of the actuator. Actuators for the reversible movement of valve flaps are known. In this case, the valve flap is respectively fixed to a drive shaft which is connected to an electric motor at a constant transmission ratio. With these known actuators, it is disadvantageous that the valve flaps can be moved only with relative difficulty after relatively long operating times as a result of soiling in the valve. The accumulated dirt causes the valve flaps to stick or cake in the valve and the valve flaps can only be released from the stuck position by means of a relatively large torque, which is often not possible or is only possible with a delay at the constant transmission ratio.